Transcript Audiometry - The Medical Post

Audiometry
Dr. Vishal Sharma
Pure Tone Audiometer
Pure Tone Audiometry
• 5 up, 10 down technique used with single
frequency tones to find hearing threshold.
• 2 correct responses out of 3 is acceptable.
• Air conduction measured for 1K, 2K, 4K, 8K,
500, 250 & 125 Hz via head phone.
• Bone conduction measured for 1K, 2K, 4K, 500
& 250 Hz via bone vibrator. Masking of other ear.
• Normal hearing for AC & BC is at 0 dB.
Symbols used in audiogram
Normal Audiogram
Pure Tone Average
Calculated by taking arithmetic mean of air conduction
thresholds at 500, 1000 & 2000 Hz (speech frequencies)
Classification of Deafness:
Goodmann & Clark
P.T.A. (dB)
Type
P.T.A. (dB)
Type
0 - 15
Normal
56 – 70
Moderate
Severe
16 – 25
Minimal
71 – 91
Severe
26 – 40
Mild
> 91
Profound
41 – 55
Moderate
Conductive deafness
Sensori-neural deafness
Mixed deafness
Diagnosis of type of deafness
Type
Air
Bone
Conduction Conduction
Air bone
gap
Conductive
Worsened
Normal
Present
Sensorineural
Worsened
Worsened
Absent
Mixed
Worsened
Worsened
Present
Low frequency conductive HL
Otitis media with effusion
Carhart’s notch (otosclerosis)
High frequency SNHL
Presbyacusis, ototoxicity, acoustic neuroma
Low frequency SNHL (Meniere)
Deafness in Meniere’s disease
Acoustic dip (Noise deafness)
Uses of pure tone audiogram
1. To find type of hearing loss
2. To find degree of hearing loss
3. For prescription of hearing aid
4. Predict hearing improvement after ear surgery
5. To predict speech reception threshold
6. A record for future medico-legal reference
Speech Audiometry
Speech Reception Threshold (S.R.T.): Minimum
intensity at which 50% of spondee (disyllable with
equal stress) words are correctly identified.
S.R.T. is normally within 10 dB of Pure Tone Average.
Speech Discrimination Score (S.D.S.): Percentage
of phonetically balanced (single syllable) words
correctly identified at 40 dB above S.R.T.
Speech Audiometry
PB max Score: Maximum SDS at any intensity.
Uses of Speech Audiometry
• Differ b/w cochlear & retro-cochlear lesions.
• Volume of hearing aid fixed at PB max score
• In functional deafness: SRT > + 10 dB of pure
tone average.
Speech Audiogram
Speech Discrimination
Hearing loss
Speech understanding
0 – 25 dB
No difficulty with faint speech
26 – 40 dB
Difficulty with faint speech only
41 – 55 dB
Difficulty with faint + normal speech
56 – 70 dB
Difficulty even with loud speech
71 – 91 dB
Only understands amplified speech
> 91 dB
Can’t understand amplified speech
Special Audiological
Tests
Tests for Recruitment
Recruitment is abnormal growth in perception
of sound intensity. Tests of recruitment are
done to diagnose a cochlear pathology.
Tests used are:
1. Short Increment Sensitivity Index (SISI) Test
2. Alternate Binaural Loudness Balance (ABLB) Test
S.I.S.I. Test (Jerger, 1959)
• Continuous tone given 20 dB above
hearing threshold & sustained for 2 min.
• Every 5 sec, tone intensity increased by 1
db and 20 such blips are given.
• SISI score = % of blips heard.
•
70-100 % in cochlear deafness
•
0-20 % in conductive & nerve deafness
A.B.L.B. Test (Fowler, 1936)
Pure tone is presented alternately to deaf &
normal ear. Intensity heard in normal ear is
adjusted to match with deaf ear. Test started 20
dB above threshold in normal ear & repeated with
10 dB raises till loudness is matched in both ears.
Initial difference is maintained, decreased &
increased in conductive, cochlear & retrocochlear lesions respectively.
Laddergram in A.B.L.B. test
Threshold Tone Decay Test
• Olsen & Noffsinger (1974)
• Detects abnormal auditory adaptation due to
nerve fatigue caused by a retro-cochlear lesion.
• Pure tone presented 20 dB above hearing
threshold, continuously for 1 min. If pt stops
hearing earlier, intensity ed by 5 dB & restart.
•
Test continued till pt hears tone continuously
for 1 min or intensity increment (decay) > 25 dB
Interpretation
Tone Decay
Pathology
dB
Type
0-5
Absent
Normal
10-15
Mild
Cochlear
20-25
Moderate
Cochlear
Severe
Retro-Cochlear
> 25
Impedance Audiometry
Impedance Audiometer Probe
A = oscillator (220 Hz). B = air pump
C = microphone to pick up reflected sound
Impedance Audiometry
1. Tympanometry
2. Acoustic reflex (Stapedial reflex)
Principles of Tympanometry
a. Less compliant T.M. reflects more sound.
b. Maximum compliance of T.M. denotes equal
pressure in E.A.C. & middle ear.
Tympanogram parameters
Adult
Child
Compliance
0.5 – 1.75 ml
0.5 – 1.75 ml
Middle ear
pressure
+ 100 to - 100
Deca Pascal
+ 60 to - 100
Deca Pascal
1.0 – 3.0 ml
0.5 – 2.0 ml
External
Auditory Canal
volume
Tympanogram Types (Jerger)
Types of Tympanogram
Type
Pressure
Compliance
Seen in
A
Normal
Normal
Normal ME
As
Normal
Decreased
Otosclerosis
Ad
Normal
Increased
Ossicular
discontinuity
B
Nil (flat curve)
Nil (flat curve)
Fluid in ME, TM
perforation
Negative
Normal
ET obstruction
C
Type A
Type As
Type Ad
Type B (fluid in middle ear)
EAC volume = 1.8 ml
Type B
(T.M. perforation, grommet)
EAC volume = 3.2 ml
Type B (E.A.C. obstruction)
EAC volume = 0.4 ml
Type C
Acoustic Reflex
Loud sound > 70 dB above hearing threshold,
causes B/L contraction of stapedius muscles,
detected by tympanometry as se in compliance.
Uses of Acoustic Reflex
1. Objective hearing test in infants & malingerers
2. Presence of reflex at <60 dB above threshold is
seen in cochlear lesion due to recruitment
3. Reflex amplitude decay of > 50 % within 10 sec
is seen in retro-cochlear lesion
4. Absence of reflex seen in facial nerve lesion
proximal to stapedius nv & in severe deafness
5. I/L reflex present, C/L absent in brainstem
lesion
B/L reflexes present
Stapedial reflex absent
Acoustic Reflex Decay
Electro-cochleography
Measures auditory stimulus related cochlear
potentials by placing an electrode within external
auditory canal / on tympanic membrane / trans-
tympanic placement on round window.
3 major components:
a. Cochlear microphonics: from outer hair cells
b. Summating potential: from inner hair cells
c. Compound Action potential: from auditory nerve
Trans-tympanic electrode
Electro-cochleography
findings in Meniere’s disease
• Summation potential : compound action
potential ratio > 30 %
• Widened waveform
• Distorted cochlear microphonics
SP – AP Waveform
Cochlear Microphonics
SP/AP
> 30 %
Normal
Distorted CM
Otoacoustic Emission (Kemp echoes)
Sounds generated within normal cochlea due to
activities of outer hair cells.
Types: 1. Spontaneous: absent in > 25 dB HL
2. Evoked: transient; distortion product
Applications: Objective & non-invasive test for:
1. Hearing screening in neonates
2. Evaluation of non-organic hearing loss
Otoacoustic Emissions (OAE)
• Spontaneous OAE: Sounds emitted without stimulus
• Transient evoked OAE: Sounds emitted in response
to click stimulus of very short duration
• Distortion product OAE: Sounds emitted in
response to 2 simultaneous tones of
different frequencies & intensities
•
Sustained-frequency OAE: Sounds emitted in
response to a continuous tone
Normal Spontaneous OAE
Normal Transient evoked OAE
Normal Transient evoked OAE
Normal Distortion Product OAE
Early detection of N.I.H.L.
Early stage N.I.H.L.
Advanced stage N.I.H.L.
Malingering of N.I.H.L.
Auditory Evoked Potentials
Auditory Evoked Potentials
• Auditory Brainstem Response: 1.5-10 ms post
stimulus; originates in 8th cranial nerve (waves I & II)
up to lateral lemniscus & inferior colliculus (wave V)
• Middle Latency Response (MLR): 25-50 ms post
stimulus; arises in upper brainstem & auditory cortex
• Slow Cortical Response: 50-200 ms post stimulus;
originating in auditory cortex
Brainstem Evoked Response
Audiometry (B.E.R.A.)
Auditory evoked neuro-electric potentials
recorded within 10 msec from scalp electrodes.
Applications: Objective test
1. Hearing threshold for uncooperative pt / malingerer
2. Hearing threshold in sleeping / sedated / comatose
3. Diagnosis of retro-cochlear pathology
4. Diagnosis of C.N.S. maturity in newborns
5. Intra-op monitoring of auditory function
Hearing test of comatose pt
Anatomy of B.E.R.A. waves
B.E.R.A. waves
Normal inter-wave latencies
Cortical Evoked Response Audiometry
(CERA) or P1-N1-P2 response
• good frequency specificity over speech
frequency range (500-3000 Hz)
• recorded from higher auditory level than BERA,
so less subject to organic neurologic disorders
• CERA must be done to evaluate accurate
hearing threshold in pt with flat audiogram &
hearing threshold of > 25 dB at 500 Hz
Multiple Auditory Steady-state
Evoked Response audiometry
• Are responses to rapid stimuli where brain response to
one stimulus overlaps with responses to other stimuli
• Slow rate responses (<20 Hz) arise in cortex & faster
rate responses (>70 Hz) originate in brainstem
•
Gives rapid, frequency specific & objective hearing
assessment by giving 4 continuous tones to each ear
Multiple Auditory Steady-state
Evoked Response audiometry
Audio Test
Cochlear
Retro-cochlear
Speech
Audiometry
S.I.S.I.
S.D.S. = 60-80 %
Positive (> 70 %)
< 40 %, Roll over
phenomenon
Negative
A.B.L.B.
laddergram
Tone decay
Converging
Diverging
Negative (< 25dB)
Positive (> 25dB)
Reflex at < 60 db
SL; Decay absent
< 4.2 msec
Reflex at > 70 db
SL; Decay present
> 4.2 msec
Stapedial reflex
B.E.R.A.
(Wave V latency)
Thank You